Dual 867MHz Is Now Dual 800MHz After Motherboard Replacement?

Discussion in 'Mac Pro' started by ghetto3jon, Nov 4, 2009.

  1. ghetto3jon macrumors newbie

    Joined:
    Oct 29, 2009
    #1
    so i replaced the motherboard on my dual 867MHz G4 MDD.

    the computer turns on now, and i did a fresh 10.4.11 install...but i noticed that it says "Dual 800" instead of "Dual 867" in my "About This Mac" now. i typed "sysctl hw.cpufrequency" in the terminal and discovered that it is actually running at 800MHz, and not 867MHz.

    so why did i lose 67MHz with a new motherboard? it was the correct motherboard (820-1445-A)...any ideas?
     
  2. lannister80 macrumors 6502

    lannister80

    Joined:
    Apr 7, 2009
    Location:
    Chicagoland
    #2
    Hmm, I know PMG4 clock speeds (at least on MDDs) are controlled by a series of resistors on the motherboard.

    For instance, if I were to upgrade my MDD G4 1.25x1 to a 1.25x2, I'd need to remove a few of the resistors to correct the clock.

    Could it be that you got a motherboard from a 800MHz machine that still happens to work with your processor?
     
  3. ghetto3jon thread starter macrumors newbie

    Joined:
    Oct 29, 2009
    #3
    a good thought...but i'm 100% positive that i replaced the motherboard with the same exact one (820-1445-A).

    i zapped the PRAM, and reset the PMU multiple times...no help.

    in fact, to my knowledge, apple didn't even make a dual 800MHz MDD computer...so it's even more strange.
     
  4. hansolo669 macrumors regular

    Joined:
    Oct 5, 2009
    #4
    try looking at the resitors, maby theve been tamperd with. its a long shot but worth a try. if the resitros have been moved/removed...then we will need more help:p happy:apple:
     
  5. CubeHacker macrumors 65816

    CubeHacker

    Joined:
    Apr 22, 2003
    #5
    The resistors should be on the CPU daughtercard, not the motherboard, as shown here:
    http://bitsandpieces.info/Multipliers.htm

    I honestly can't think of a reason the CPU speed would change unless those multipliers changed.

    Unless... perhaps someone tried that "open firmware overclock trick" on that motherboard. Perhaps if you reset the PMU and firmware, it would go back to the default speeds?
     
  6. ghetto3jon thread starter macrumors newbie

    Joined:
    Oct 29, 2009
    #6
    i appreciate all of the input.

    one thing to point out: i was mistaken. this machine was NOT a dual 867MHz, it was a dual 1GHz. i have so many of these machines around here, i get them confused...

    so this computer went from dual 1GB to dual 800MHz when i changed the motherboard. and since the processor module didn't change, it can't have anything to do with those resistors.

    i did reset the PMU and nothing happened. CubeHacker, you mentioned resetting the firmware? how is that done?

    (i also tried a fresh OSX installation, and that didn't help either. so it's definitely not software related).
     
  7. ghetto3jon thread starter macrumors newbie

    Joined:
    Oct 29, 2009
    #7
    so someone on another forum pointed out this:

    "so, maybe this is just a coincidence, but a 1 GHz CPU from a 167 mobo installed in a 133 mobo would operate at a proportional 133/167 bus speed ratio = 800 MHz."

    but why then did the computer run at full dual 1GHz before i replaced the motherboard? now again, i'm 100% percent positive that i replaced the motherboard with the same exact one that was in there...but maybe the one that was in there was somehow modified to allow the computer to run at dual GHz? that's what i'm thinking now...
     
  8. ghetto3jon thread starter macrumors newbie

    Joined:
    Oct 29, 2009
  9. lannister80 macrumors 6502

    lannister80

    Joined:
    Apr 7, 2009
    Location:
    Chicagoland

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